1. Field of the Invention
The present invention relates to a device and a method for processing an image, and, in particular, to an image processor that converts information embedded in a print medium in an unreadable format to an electronic form and erases and updates the information embedded in the unreadable format, and also to an image processing method for reading, erasing and updating information embedded in an unreadable format.
2. Description of the Background Art
One of the recent social problems is a number of information-leakage incidents having occurred from, for example, printed documents. In particular, the information-leakage incidents from printed documents are described in “2004 Investigative Report on Information Security Incidents”, Japan Network Security Association (JNSA), January 2006. The report, which is herein referenced merely as a document teaching the background art, says that such incidents occupy about as much as 46% of the entire information-leakage incidents. Immediate measures are required.
As measures against information leakage from printed materials, printed materials may be provided with a function of identifying the routing path of the printed materials, thereby facilitating diagnosis of information leakage. This can effectively exert suppression of information leakage. That function includes, for example, a process of embedding in an unreadable format information on a person and a place concerned with printing the printed materials. In order to identify the leakage path, it is preferable to be able to derive, from the printed materials, information on all people and places concerned with the distribution of the printed materials. Technology to embed into printed materials in an unreadable format information on a historical record obtained on a routing path of a printed material till it is actually printed is disclosed by, for example, JP Patent Laid-Open Publication No. 2005-286963, US Patent Application Publication No. US2003/0021442A1 to Suzaki, and JP Patent Laid-Open Publication No. 2005-269551.
JP 2005-286963 discloses a scheme in which a plurality of small dots are arranged to record information. The small dots include an area-prescribing dot which prescribes a unit area that represents information, and an information dot which represents information using a relative position in the unit area prescribed by the area-prescribing dot, thus being arranged to embed information. Information is read out by detecting an area-prescribing dot to know a unit area, recognizing the position of the information dot in the unit area, and determining the relative position of the information dot from the unit area.
Suzaki and JP 2005-269551 disclose a scheme in which a dot pattern, referred to as a signal pattern, is provided in which dots are arranged with the propagation direction and wavelength of waves changed so that each signal pattern is provided with one or more symbols and the signal patterns are combined and arranged to thereby embed information. Information is read out by detecting a signal pattern wave using a Gabor filter to identify a symbol, and decoding information from the resulting symbol using an error correction code and a determination on majority rule.
In any of the above schemes, the patterns including dots carrying information have different shapes depending on the embedded information, although the patterns are averagely almost uniform in concentration distribution. That causes information, when embedded even in the entire background of a document image, to be visually inconspicuous, thus not significantly affecting the readability of the original document image. The dots of a tint-block may be changed in diameter and density so as to vary the concentration without affecting the embedded information, thereby sometimes intentionally drawing a picture and a letter on the tint-block.
With reference to FIGS. 1A, 1B, and 1C of the accompanying drawings, Suzaki and JP 2005-269551 disclose signal patterns specific thereto. FIG. 1A shows an example of signal pattern recording binary information “1”. FIG. 1B shows an example of signal pattern recording binary information “0”. FIG. 1C shows an example of pattern that is formed when the embedded information is three rows by four columns, corresponding to 12 bits.
Such signal patterns are repeatedly subject to error correction encoding and information processing before being embedded in order to avoid failure in reading out information caused by a corrugation or a stain of printed materials or copying, aging or cutting out printed materials. FIG. 2 schematically shows an example where 256-bit information is embedded.
With reference to FIG. 2, 256-bit information 500 is divided into four sets of 64-bit information 502, 504, 506, and 508. Each of the sets of 64-bit information is added with 4 bits of index information 510 different from each other and 12 bits of page information 512 common to each other for identifying a page to thereby produce four sets of 80-bit information 514. The index information 510 may be represented by, for example, ‘0000’, ‘0001’, ‘0010’, or ‘0100’.
Each 80-bit information is encoded to an error correction BCH (144, 80) code (Bose-Chaudhuri-Hocquenghem) 516, which is 8-bit correctable and has its code length of 144 bits. The encoded information is represented by blocks 518, 520, 522 and 524, each of which is formed by 12 rows by 12 columns consisting of 144 bits and contains information different from each other. When a signal pattern for recording information has a size of 18 rows of 18 pixels, one block containing 144-bit information has its size of 216 rows of 216 pixels.
When information is embedded in an A4 size sheet, for example, an A4 sized image of 300 dpi (dots per inch) has 2500 rows of 3500 pixels. The A4 sized sheet thus has 11 sets of 16 blocks, corresponding to 176 blocks, arranged thereon. With reference to FIG. 3, 256-bit information is embedded in four types of information blocks A, B, C and D, each of which are repetitive 44 times (176/4=44).
In order to read out the 256-bit information thus embedded in the A4 sheet in the ideal condition where it is not necessary to consider the letters, printing distortion, scanning distortion and stain on the document, it is sufficient to readout the information from the area corresponding to four of the blocks on the sheet.
Unfortunately, in the above methods, it is hard to fetch information on the historical record of, for example, the copy operator who copied the documents and the equipment and places on most of the routing paths. In order to have the information during the copying held in the printed materials as a historical record, it is required to update the embedded information during the copying by the copier. In the technologies disclosed by JP 2005-286963, Suzaki and JP 2005-269551, information is represented by visible dots, which are apt to be easily duplicated and the information embedded in an unreadable format is hard to update. Because, when the updated information is embedded in a copy, the dots holding the original information become an obstacle to forming a pattern representing the correct information on the print material.
In addition, copying slightly degrades a watermark pattern. It is thus hard to avoid the degradation through repeated copying. Furthermore, when printed materials are duplicated as magnified or reduced, watermarks are significantly degraded. In practice, therefore, the magnification/reduction during copying may be inhibited or the number of copies for enabling information to be read may be limited by the performance.
A technology is thus required by which a signal pattern printed in a printed document in an unreadable format may, when scanned, be erased from the scanned image and renewed information may be embedded thereinto.